Python is an interpreted, high level language that is freely available for developing applications. And Curses or ncurses is a library that lets you program GUIs in Python. Curses library is about window programming within the boundaries of the terminal. Using this library one can manipulate data, create a sub window or create multiple windows of all sizes that overlap.
A programmer can use colors, mouse pointer, etc on screen even if the 'X' server (in Linux or Unix) is not running. For eg, when you're logged in to Linux on a terminal where neither X is installed nor you have the privilege to run it; you can use Curses to write applications which can directly run on the terminal with Mouse and color support.